Powerful reductant for decontamination of groundwater and surface streams

ABSTRACT

The disclosed invention relates to a composite material for use in recovery of radionuclides, metals, and halogenated hydrocarbons from aqueous media. The material has very high surface area, and includes nanometer sized, zero-valent iron on a support. The material can be used to remediate aqueous media which have contaminants such as radionuclides, metals and halogenated hydrocarbons from aqueous media.

This is a divisional, continuation-in-part of application Ser. No.09/007,851 filed on Jan. 15, 1998 now abandoned.

FIELD OF THE INVENTION

The invention relates to separation of heavy metals, radionuclides, andhalogenated hydrocarbons from aqueous media

BACKGROUND OF THE INVENTION

Heavy metals, radionuclides, and halogenated hydrocarbons constitutemajor contaminants in the clean-up and decontamination of aqueous waste.Virtually every site or aqueous stream that requires remediationcontains contaminants from at least one of these three groups.

For example, many of the Superfund sites administered by the U.S.Environmental Protection Agency involve heavy metals such as lead,mercury, or chromium from factories previously occupying these sites.The U.S. Department of Energy's waste sites at Hanford, Washington, andat the Savannah River, South Carolina contain vast amounts of aqueouswaste with significant amounts of radionuclides such as strontium-90,cesium-137, and technetium-99 are present. Halogenated hydrocarbons suchas perchlorethylene (PCE) and trichlorethylene (TCE) are commonindustrial solvents still in wide use today, e.g. drycleaners. Thesehalogenated hydrocarbons are highly toxic and are likely carcinogenswith safe drinking water limits of less than 10 parts per billion. Anaccidental spill of these chlorinated hydrocarbons could cause serioushazardous risks to municipal water supplies.

Previously, removal of these types of contaminants required veryexpensive treatment procedures. These procedures primarily usepump-and-treat methods wherein water was pumped out of the soil,treated, and then pumped back into the ground. In addition, expensivereagents such as ethylene diaminetraacetic acid (EDTA) or expensivematerials such as ultrafilters are required for these treatments.

In the case of halogenated hydrocarbon contaminants, a recentdevelopment which has garnered strong interest is the use of ironfilings or powders, or iron sulfide(pyrite), for in-situ treatment ofcontaminated groundwater streams. The iron (or the pyrite) has beenfound to degrade hydrocarbons by reductive elimination and/or reductivedehalogenation of the parent compound and its daughter products. In use,the iron (or pyrite) is placed in a trench or a well that is locatedperpendicular to the flow of the groundwater, with the intent of leavingthe reagent permanently in place. While this method obviates thenecessity for maintainence, and is much less expensive thanpump-and-treat methods, the relatively low reactivity of the iron orpyrite requires large amounts of reagent to achieve completedecontamination. Thus, if iron filings were used, a large emplacementwould be required, entailing large initial capital costs.

In the case of radionuclides, treatment of radionuclide contaminationentails special considerations. Radionuclide contaminants invariablyinvolve a national government, have little or no margin for losses tothe environment, and must be recovered in a form suitable for handlingand further processing for long-term storage.

A radionuclide that is of special concern is technetium. Technetium isan artificial, radioactive element that is a by-product of both weaponsdedicated and energy generating nuclear fission plants. It presents aparticular difficulty in that it commonly forms the pertechnetate anion(TcO₄ ⁻). It is of global concern as it is not only a contaminant at theDepartment of Energy's Hanford, Savannah River, and Oak Ridge sites, butis also present at the Chernobyl disaster site, and continues to beproduced by fission plants throughout the world.

Technetium (Tc) removal is a high priority need. Waste separation,pretreatment, and vitrification processes for technetium removal involveseparation into solid high level waste (HLW) and low level waste (LLW)fractions. The latter contains most of the Tc, predominantly in the +7oxidation state as the pertechnetate ion (TcO₄ ⁻). Vitrification ofthese waste fractions is problematic because Tc⁷⁺ compounds are volatileat high temperatures, and the presence of large quantities of nitrateand nitrate in the LLW ensures that the melts remain oxidizing.

Methods of extracting Tc from the aqueous media such as LLW prior toconcentration and vitrification are urgently needed to address thisvolatility problem, as well as to reduce the total volume of vitrifiedwaste. These needs are driven by both safety and cost considerations.

While other radionuclides such as strontium and cesium are present inlow-level waste form as cations and can be sorbed onto clays and micas,or, under some conditions, precipitated with tetraphenylborate, thepertechnetate ion carries a negative charge and exhibits little or noneof the usual sorptive precipitation behavior of metal ions. Thus, it isvery difficult to contain and process technetium with any previouslyexisting technology.

A need therefore exists for remediation of radionuclides, metalcontaminants and halogenated hydrocarbons in groundwater. A particularneed exists for remediation of radionuclides such as technetium andheavy metals such as such as chromium, lead, mercury and titanium ingroundwater.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron micrograph, 20 KV×3,500 of Ferragelparticles showing metallic iron on silica.

FIG. 2 shows the percentage of original amount of 0.017 M rheniumpresent in solution as perrhenate anion.

FIG. 3(a) shows a scanning electron micrograph, 20 KV×10,000 of Ferragelcoated with rhenium in accordance with the invention with rhenium at theend of Example 1.

FIG. 3(b) shows EDX analysis of elemental makeup of the product shown inFIG. 3(a)

FIG. 4 shows the percentage of original amount of 4.998 mM chromiumpresent as hexavalent chromium ion.

FIG. 5 shows the percentage of the original amount of 4.988 mM mercuryremaining in solution as divalent mercury ion.

FIG. 6 shows the percentage of the original amount of 4.951 mM leadremaining in solution as divalent lead ion.

FIGS. 7(a)-(c) show surface modifying layers on Ferragel.

SUMMARY OF THE INVENTION

The disclosed invention relates to a composite material that includesthe reaction product of a ferrous salt, preferably FeSO₄—7H₂O, and analkali borohydride, preferably NaBH₄, NaBH₃CN, and B₂H₆, most preferablyNaBH₄ NaBH₄ is a strong, water-soluble reducing agent.

In a further aspect, the invention relates to a method for manufactureof a composite material that has strong reducing properties. The methodentails forming a solution of a water-soluble ionic salt of Fe in waterin the presence of a support material, and adding an alkali borohydridein a sufficient amount to form a precipitate of support material havingzero valent Fe thereon.

In yet another aspect, the invention relates to remediation ofcontaminants from an aqueous liquid by treating that liquid with acomposite material that includes the reaction product of a metal salt,preferably a ferrous salt, most preferably FeSO₄—7H₂O, and an alkaliborohydride, preferably an alkali borohydride such as NaBH₄, NaBH₃CN,and B₂H₆.

Having summarized the invention, the invention will now be described indetail by the following description and non-limiting examples.

DETAILED DESCRIPTION OF THE INVENTION

The novel supported, reducing materials of the invention, hereinafterreferred to as “Ferragels”, are an activated form of primarily,zero-valent, nanometer size metal(s) on a support material thatpreferably has a high surface area. The zero-valent metal that is sorbedonto the support material is about 25% to about 75% by weight,preferably about 40% to about 60% by weight of the combined weight ofthe support material and the nanometer scale metal(s). The zero-valentmetal that is bound to the support material has an average particle sizeof about 5 nm to about 50 nm, preferably about 5 nm to about 15 nm. TheFerragel particles are characterized by extremely high surface areasthat are much greater than the surface areas of commercially availableFe powder. Surface areas of the metals used in Ferragels range fromabout 10 m²/g to about 45 m²/g. In contrast, surfaces areas ofcommercially available Fe powder that has a particle size less thanabout 10 micron is only about 0.9 m²/gm. Preferably, iron is theactivated form of zero-valent metal on the support material. Otherzero-valent metals, i.e., dopant metals, may be present with iron on thesupport material. Examples of useful dopant metals include but are notlimited to transition metals such as Pd, Pt, Zn, Ni, V, Mn, Cu, Pr, Cr,Co, and non-transition metals such as Sn and Pb. Preferred dopant metalsinclude Pd, Pt, Zn, Mn, V, Cr, Cu, Co, and Ni. Most preferred dopantmetals include Pd, Pt, Zn, Co and Mn. Dopant metals may be present inamounts of up to about 30% by weight of the combined weight of thesupport material and the bound metals. Dopant metals are especiallyuseful when the Ferragel is employed in environments where thezero-valent iron might be readily oxidized by species other than thetargeted contaminants.

The Ferragel materials of the invention are stable and non-toxic. TheFerragels are highly reactive, due in part to their very high surfacearea to volume ratio. The Ferragel materials of the invention can beprovided in a wide range of compositions of iron, dopant metals andsupport materials to remediate a variety of heavy metals, radionuclides,and halogenated hydrocarbons from aqueous media such as aqueous liquids.The Ferragel materials of the invention may include zero-valent iron,optionally doped with the aforesaid dopant metals, on silica, as well aszero-valent iron optionally with the aforesaid metal dopants on othersupport materials such as metal oxides and polymeric materials. Usefulpolymeric support materials include but are not limited to styrofoam,polyethylene, polypropylene, polystyrene, and polyester. A mostpreferred composition of Ferragel is zero-valent iron on silica supportparticles.

Ferragel compositions of iron-on-silica, as shown in FIG. 1, arefinely-grained, zero-valent iron on silica particles. Ferragel materialsof iron-on-silica may be provided in a wide range of weight ratios ofsilica to iron particles. Useful weight ratios of silica to iron mayvary from about 1:1 to about 100:1, preferably about 1:1 to about 1:7,most preferably about 2:5. Despite the high degree of dispersion, veryhigh loadings of an active metal such as Fe can be achieved. Forexample, the Ferragel shown in FIG. 1 is approximately 50% Fe by weight.

Support materials suitable for use in Ferragel can be any materialcapable of supporting iron and dopant metals and which is most usuallyinert to the reduction/oxidation reactions which may occur during theextraction and remediation processes in which the Ferragel is employed.Preferred support materials are porous and have a high surface area.Useful support materials include but are not limited to silica gel,sand, gravel, metal oxides such as titanium oxide, tin oxide andzirconium oxide; polymeric foams such as Styrofoam and polyurethane,polymer resins, polyethylene, polypropylene, polystyrene, polyesters,silicones, and polyphosphazenes and mixtures thereof. Other usefulsupport materials include metals such as Pd, Pt, Zn, Ni, V, Mn, Cu, Pr,Cr, Co, Sn and Pb. The support material typically is about 20%-85% byweight of combined weight of the support material and deposited metals,preferably from about 40% to about 60% by weight by weight of combinedweight of the support material and metals. Most preferably, the supportmaterial is silica gel.

Useful water soluble salts of Fe that yield Fe²⁺ ions such as ferroussulfates, chlorides, borates, perchlorates, and nitrates, preferablysulphates and chlorides, most preferably FeSO₄—7H₂O, either by itself orin admixture with salts of metal dopants, may be employed in manufactureof Ferragel.

Preferred salts of metal dopants which may be employed with the salts ofFe include water soluble salts of Pd, Pt, Zn, Sn, Mn such as Pdsulfates, Pd nitrates, Pd chlorides, Pd acetates, Pt sulfates, Ptnitrates, Pt chlorides, Pt acetates, Zn sulfates, Zn nitrates, Znchlorides, Zn acetates, Mn sulfates, Mn nitrates, Mn chlorides, and Mnacetates. Other salts of metal dopants which may be employed with theiron salts include, for example, water soluble salts of V, Cr, Cu, Co,and Ni such as V sulfates, V nitrates, V chlorides, V acetates, Crsulphates, Cr nitrates, Cr chlorides, Cr acetates, Cu sulphates, Cunitrates, Cu chlorides, Cu acetates, Co sulphates, Co nitrates, Cochlorides, Co acetates, Ni sulphates, Ni nitrates, Ni chlorides, and Niacetates.

In preparation of the Ferragel materials of the invention, a watersoluble ionic salt of Fe that yields Fe²⁺ ions such as ferroussulphates, chlorides, borates, and perchlorates, preferably sulphates orchlorides, either by itself or in admixture with salts of metal dopants,is dissolved in water in the presence of a support material. The watersoluble salt of Fe may be mixed with salts of dopant metals to provide adoped Ferragel to maximize effectiveness for specific target compoundsand/or environments. For example, soluble salts of dopant metals such asPd, Pt, Zn, Sn, Mn may be mixed with the water soluble salt of Fe.Examples of useful soluble salts of dopant metals include Pd sulfates,Pd nitrates, Pd chlorides, Pd acetates, Pt sulfates, Pt nitrates, Ptchlorides, Pt acetates, Zn sulfates, Zn nitrates, Zn chlorides, Znacetates, Mn sulfates, Mn nitrates, Mn chlorides, and Mn acetates, aswell as water soluble salts of V, Cr, Cu, Co, and Ni such as V sulfates,V nitrates, V chlorides, V acetates, Cr sulphates, Cr nitrates, Crchlorides, Cr acetates, Cu sulphates, Cu nitrates, Cu chlorides, Cuacetates, Co sulphates, Co nitrates, Co chlorides, Co acetates, Nisulphates, Ni nitrates, Ni chlorides, and Ni acetates. The salts ofmetal dopants may be employed in a wide range of weight ratios to theiron salts. Ratios of salts of metal dopants to Fe salts may vary fromabout 1:1 to about 1:100 by weight, preferably about 1:2 to about 1:40by weight, most preferably about 1:5 to about 1:20.

Organometallic salts of dopant metals such as amine/ethylene/COcomplexes of those metals also may be employed with the water solublesalts of Fe. Examples of organometallic salts which may be employedinclude but are not limited to complexes of Pt, Pd and Rh such astetraamine Pt salts and Rh salts.

The salt(s) of iron, optionally with salts of dopant metal(s), andsupport materials are stirred in an aqueous solution until well mixed. Astrong reducing agent then is added in a sufficient amount to form aprecipitate of support material having zero valent metal thereon. Thereducing agent may be an alkali borohydride such as NaBH₄, cyanoderivatives of NaBH₄ such as NaBH₃CN, and B₂H₆, preferably NaBH₄. Afterthe precipitate is formed, it is stirred in the remaining solution, andfiltered. The collected precipitate then is dried.

Both acidic and alkaline aqueous solutions may be employed inmanufacture of Ferragels. Accordingly, the pH of the solution employedmay vary from about 4.5 to about 13. Most preferably, mild solutionswhich have a pH of about 6.5 to about 7.5 are employed. These mildsolutions are formed by dissolving the salts of iron and/metal dopantsalts into an aqueous solution containing at least one support material.When alkaline solutions, especially alkaline solutions which have a pHgreater than about 10, are employed, those alkaline solutions are formedby dissolving soluble hydroxides such as hydroxides of Na, Li, Cs, K,Ba, Rb, and NH₄ ⁺, preferably Na or K, as well as mixtures thereof, oralkali bicarbonates such as sodium bicarbonate in an aqueous solutioncontaining support material.

In a most preferred aspect of the invention, a Ferragel composition ofiron on a silica support material is formed. This Ferragel compositionis formed by adding ferrous sulfate to a slightly acid aqueous mixturescontaining silica gel that has a pH of about 6.2 to about 6.9 to providea weight ratio of silica to iron of about 2:5, preferably about 1:1 toabout 1:7, most preferably about 1:1. The ferrous sulphate and silicagel are stirred in the mild solution until the salt is dissolved,preferably completely dissolved. The pH of the solution is adjusted byaddition of NaOH. Then, NaBH₄ is added in sufficient amount to reducethe ferrous ions to iron metal on silica to produce a precipitate ofzero-valent iron on silica particles. The remaining solution, includingthe precipitate, is stirred for about 5 minutes to about 120 minutes,preferably about 25 minutes, and filtered. The precipitate is vacuumdried at about 5° C. to about 100° C. for about 6 hours to about 12hours. Typical vacuum pressures which may be used are about −30 psi.

Alternatively, the precipitate may be dried in an inert atmosphere ofnitrogen or argon at about 5° C. to about 100° C. for about 6 hours toabout 12 hours.

The invention is further illustrated below by the following non-limitingexamples.

Remediation of Radionuclides

To simulate the ability of Ferragels to remediate TcO₄ ⁻, perrhenate ionis used as a surrogate. Perrhenate ion is very similar in size andchemistry to TcO₄ ⁻, but is non-radioactive and more difficult to reducethan TcO₄ ⁻. As shown below, the Ferragels of the invention cansuccessfully remove perrhenate ion. Ferragels may thus be used toremediate TcO₄ ⁻ to form insoluble TcO₂. The method of the invention canperform under a wide variety of conditions, such as environments havinghigh alkalinity (3.8 M OH−), high sodium content (10.0 M Na+), and highconcentration of both nitrate and nitrite ions (3.1 and 1.7 M,respectively). The products produced by the invention may be used asfeedstock to produce low melting and reducing glasses, so thatvolatility and containment problems associated with processing of TcO₄ ⁻can be minimized.

EXAMPLE 1

Perrhenate anion.

5.1524 g of FeSO₄—7H₂O is mixed with 2.6781 g silica gel in a beakercontaining 50 mL of 0.38 M NaOH solution and stirred for 10 minutes toform a mixture. 0.7 g of NaBH₄ is slowly added to the mixture. After 24hours of stirring, 0.3 g of black solid precipitate of an iron-on-silicaFerragel is formed. This precipitate is added to 20.00 mL of solution of0.017 M KReO₄ in 3.8 M NaOH. UV-Vis spectroscopy is performed to trackthe ReO⁴⁻ content of the solution. As shown in FIG. 2, after 8.9 days,99.986% of the rhenium is precipitated onto the iron particles of theFerragel. Confirmation that the rhenium is sorbed onto the ironparticles, as shown in FIG. 3, is obtained by energy dispersive x-rayfluorescence.

Remediation of Heavy Metals

EXAMPLE 2

Mercury.

10.0884 g of FeSO₄—7H₂O is stirred with 4.2850 g of silica gel in 75 mLof 0.38 M NaOH solution for 2 hours. 0.6535 g of NaBH₄ is added andstirring continued for 1 day. The resulting iron-on-silica Ferragelsolids are filtered and dried in vacuum. For sample “Hg-1”, 0.1011 g ofdried Ferragel is added to 20.00 mL of 4.988 mM HgCl₂ solution. Forsample “Hg-2”, 0.1504 g of dried solids is added to 20.00 mL of HgCl₂solution. Mercury content of the solution is determined by UV-Visspectroscopy following extraction of a 1.000 mL aliquot intobiphenylthiocarbazone (0.0100 g/L) in chloroform. As shown in FIG. 5,After 5.84 days, only 6.23% of the original mercury remained in solutionfor sample Hg-1, and less than 0.01% remained in solution for sampleHg-2.

EXAMPLE 3

Lead

Dried iron-on-silica Ferragel solids were obtained as prepared inExample 2. For sample “Pb-1”, 0.1012 g of the dried Ferragel solids areadded to 20.00 mL of 4.951 mM Pb(C₂H₃O₂)₂ solution, while 0.1515 g ofthe dried Ferragel solids are added to another 20.00 mL of the leadacetate solution for sample “Pb-2”. Lead content is determined by UV-Visspectroscopy following extraction of a 1.000 mL aliquot intobiphenylthiocarbazone (0.0100 g/L) in chloroform. As shown in FIG. 6,After 3.98 days, 2.33% of the original lead ions is found in the samplePb-1 solution, while less than 0.01% of the original amount of lead usfound in the sample Pb-2 solution.

EXAMPLE 4

Chromium

Dried iron on silica Ferragel solids are prepared as in Example 2. Forsample “Cr-1”, 0.1007 g of the dried Ferragel solids are added to 20.00ML of 4.998 mM CrO₃ solution. For sample “Cr-2”, 0.1504 g of the driedFerragel solids are used. Chromium content is determined by UV-Visspectroscopy. As shown in FIG. 4, after 5.87 days, 15.78% of theoriginal chromium remains in sample Cr-1, while 5.20% remains in sampleCr-2.

In situ remediation of underground streams

An underground stream contaminated by halogenated organics, heavymetals, or radionuclides is treated. In doing so, a trench is dug acrossthe path of the underground stream and the trench is filled withFerragel particles. The trench is dug so that substantially all of theunderground stream passes through the Ferragel. The trench containssufficient Ferragel to react with the entire amount of contaminant inthe stream without further replacement of the Ferragel. The metalcomponent of the Ferragel is most preferably iron, but may be anothermetal or combination of metals. The support material used in theFerragel is of a size appropriate to leave the overall porosity of theenvironment, and the flow pattern of the stream, unchanged. The supportmaterial used is preferably a porous silica, but other support materialssuch as metal oxides or polymer resins may be used. The trench may firstbe lined with a barrier, such as polyethylene cloth. The filled trenchthen is covered with earth. It is intended that no further work need beperformed for decontamination of the underground water flow downstreamfrom trench containing the Ferragel. However, solid products resultingfrom the remediation process, e.g., metals or metal oxides nowprecipitated on the Ferragel, may be collected by reopening the trench.

EXAMPLE 5

100 g of FeSO₄—7H₂O is dissolved in 500 mL of water at pH 6.9. Then, 40g of silica gel is stirred in. 6.5 g of NaBH₄ then is added and stirredfor 30 minutes. Any resulting Ferragel is placed in a vertical cutperpendicular to an underground flow containing 20 ppm Tl(III).

Remediation of contaminated tank wastes

Ferragel may be placed in the path of a pumped flow by encasing theFerragel inside a tank in a manner similar to the packing of a packedcolumn, When the tank has been pumped empty of liquid, the Ferragel maybe collected or disposed of. Alternatively, Ferragel may be addeddirectly to the tank having waste material therein. Once thecontaminants have been removed, the liquid is decanted or filtered,leaving the dry solid remediated products ready for disposal. Eithertechnique may be used to remediate halogenated organics, metal ions,radionuclides or combinations thereof.

EXAMPLE 6

100 g of FeSO₄—7H₂O is dissolved in 500 mL of water at pH 6.9. Then, 40g of silica gel is stirred in. 6.5 g of NaBH₄ then is added to themixture and stirring continues for 30 minutes. Any resultingiron-on-silica Ferragel solids are dried, packed into a cylinder andplaced in a stream that contains 50 ppm Cr(VI), 10 ppm polychlorinatedbiphenyls and 30 ppm perchloroethylene so that the cylinder length isparallel to the stream flow. Upon termination of the reaction, any CrO₂containing solids produced are filtered and dried.

EXAMPLE 7

The procedure of Example 6 is followed except that Ferragel particlesare added directly to a tank that contains 50 ppm Cr(VI), 10 ppmpolychlorinated biphenyls and 30 ppm perchloroethylene. Upon terminationof the reaction, any CrO₂ containing solids produced are filtered anddried.

EXAMPLE 8

100 g of FeSO₄—7H₂O is dissolved in 500 mL of water at pH 6.9. Then, 60g of stannic oxide are stirred in. Thereafter, 6.5 g of NaBH₄ is addedto the mixture and stirring continues for 25 minutes. Any resultingiron-on-silica Ferragel particles are dried in vacuum and placed into atank containing 0.017 M TcO₄ ⁻. The pH of the tank is about 13.5, and itis about 10 M in sodium ions, including nitrate, carbonate, andhydroxide. Any resulting solids of predominately TcO₂ are removed byfiltering and then vitrified.

In situ remediation of deep groundwater streams

Ferragel particles may be directly pressure-injected into the path of agroundwater stream when the stream lies too far below the surface toallow trenching to be used economically. This is useful to treatgroundwater streams which may contain, for example, uranium that areabout 400 ft. below the surface. The extremely small size of Ferragelparticles makes for greater ease of injection than milled iron powders,and is likely to cause less disruption of the porosity of the streamenvironment

EXAMPLE 9

100 g of FeSO₄—7H₂O is dissolved in 500 mL of water at pH 6.9. 6.5 g ofNaBH₄ then is added and stirred for 30 minutes. Any resulting nanoscaleiron particles are dried and pressure injected into the path of anunderground stream containing UO₂ ⁻ ions.

In situ soil remediation

Surface-derivatized Ferragels may be used for in-situ remediation ofcontaminated soils. The derivatized Ferragel is tilled into the soilsurface, and the soil surface is wetted. The surface-derivatizedFerragel combines a head group such as silanols, phosphonates,hydoxamates, or carboxylates, with a tail group that has a high affinityfor the contaminant. For instance, an alkyl chain is used to enhance thesorption of a sparingly soluble organic contaminant such astrichlorethylene to the Ferragel particles. After the Ferragel/surfacesoil mixture has been wetted, the Ferragel may move through the soil viatransport mechanisms equivalent to that of the contaminant. Thistechnique may be used in tandem with the aforementioned trenching andinjection methods to provide a barrier against any contaminant runoff.

EXAMPLE 10

100 g of FeSO₄—7H₂O and 10 g of SnCl₂ are stirred with 40 g of silicagel in 500 mL of water at pH 6.9. 6.5 g of NaBH₄ is added to the mixtureand stirring continues for 30 minutes. Any resulting iron-on-silicaFerragel solids are dried in vacuum.

The dried Ferragel solids are stirred with a solution of ethanol thatcontains dissolved hexadecylphosphonate. The weight to weight ratio ofthe dried Ferragel to the crystal hexadecylphosphonate in the solutionis 1:1. The solution is heated and stirred until the ethanol isevaporated. The resultant surface-derivatized Ferragel is scratched intothe surface of a soil contaminated with sorbed trichlorethylene. Thesurface of the soil is then wet to the depth of 10 cm.

EXAMPLE 11

The procedure of example 10 is followed with the exception that theweight to weight ratio of the dried Ferragel to the crystalhexadecylphosphonate in the solution is 5:1.

EXAMPLE 12

The procedure of example 10 is followed with the exception that theweight to weight ratio of the dried Ferragel to the crystalhexadecylphosphonate in the solution is 1:1-5.

Recovery of trace elements from aqueous streams

Ferragels may also be used in-situ to separate trace metals from anaqueous environment and concentrate them in an insoluble form for laterrecovery.

EXAMPLE 13

100 g of FeSO₄—7H₂O is stirred with 20 g of styrofoam pellets in 500 mLof water which has had its pH adjusted to 6.9 with NaOH. 6.5 g of NaBH₄is added and stirring continues for 25 minutes. Any resultingiron-on-styrofoam Ferragel is packed into an open-ended cylinder andplaced in a stream containing 30 ppb of Au ions and 300 ppb of Ag ions.The cylinder is positioned so that the length of the cylinder isparallel to the stream flow. Metallic Au and Ag may be recovered bysolvation and/or heating.

EXAMPLE 14

The procedure of example 13 is followed with the exception that theFerragel particles are made with sand as a support material.

EXAMPLE 15

The procedure of example 13 is followed with the exception that theFerragel particles are made with gravel as a support material.

EXAMPLE 16

The procedure of example 13 is followed with the exception that theFerragel particles are made with silica gel as a support material.

As described above, Ferragels of the invention may be employed to treata wide variety of waste components in an advantageous manner to extractcontaminants from both waste streams and groundwater streams. Ferragelscan be used to degrade these contaminants into innocuous compounds, orimmobilize them in forms that are compatible with conventional disposalprocedures. The great efficiency of the Ferragels of the invention forremoving waste components means that less bulk and mass of material maybe used, as compared to the need of the prior art to use iron filings,pyrite, or organic carbon. Thus, excavation and containment costs can bereduced.

The Ferragels of the invention, due in large part to their very highsurface area to volume ratio, are highly reactive. When used toremediate waste streams of heavy metals and radionuclides, Ferragelswhich include iron, optionally with dopant metal on the support materialare believed to react electrochemically with dissolved contaminate metalions and radionuclides to form insoluble products of those metals andradionuclides.

The Ferragels of the invention effectively present the zero-valent ironand dopant metal(s) to target metallic ions and halogenated hydrocarbonsin a fluid stream such as an aqueous waste stream. The supportedzero-valent metal can be used to remove metal ions, radionuclides, orhalogenated hydrocarbons from aqueous streams for treatment of surfaceand groundwater streams.

Ferragels may be employed to recover heavy metals such as Th, Hg, Pb,Cd, As, Bi, Sb, precious metals such as Cu, Ag, Au, Pt, Pd, Rh and Ir,transition metals such as Co, Cr, V, Ni, W, rare earths such as Ce, Eu,and radionuclides such as Tc, Pu, U, Np. Ferragels also may be used torecover various other metals such as Sn, Mn, Ti, Ge, In, Re, Ru, Te, Seas well as radioactive isotopes of various metals. Ferragels thus may beused to reduce divalent lead ions to metallic lead, hexavalent chromiumto insoluble lower oxidation states of chromium or to the zero-valentchromium, and heptavalent rhenium or technetium to metals or theinsoluble dioxides. Ferragels, in these applications, are believed tochemically reduce aqueous ions of contaminant metals and radionuclidesto produce insoluble compounds which replace the iron and/or metaldopants sorbed on the support materials.

Ferragels also can be employed to remediate a variety of heavy metals,radionuclides, and halogenated hydrocarbons from organic liquids such asalcohols, e.g., ethyl alcohol, ethers, tetrahydrofuran, alkanes such ashexane. The organic liquid stream includes water, preferably water in anamount of up to about 50% by weight of the organic liquid stream, morepreferably water in an amount of up to about 75% by weight of theorganic liquid stream, most preferably water in an amount of up to about90% by weight of the organic liquid stream.

Ferragels also may be used to remediate waste streams which containhalogenated hydrocarbons. During this application, it is believed thatan electron transfer reaction occurs to cause reductive hydrogenolysisor reductive elimination. During reductive hydrogenolysis, a halogenatom is removed from the halogenated hydrocarbon as an anion andreplaced with a hydrogen ion. During reductive elimination, two halogenatoms are removed from the halogenated hydrocarbon. The processcontinues until the hydrocarbon is completely dehalogenated. Ferragelsthat employ iron with tin dopant metal in a molar ratio of about 7.5:1is especially useful for dehalogenation of aqueous waste streams thatinclude perchloroethylene.

When employed to remediate halogenated hydrocarbons, Ferragels arebelieved to reductively degrade halogenated hydrocarbons such as carbontetrachloride, trichlorethylene (TCE), and tetrachlorethylene (PCE) inaqueous streams by degrading them into the base hydrocarbon, e.g.methane in the case of carbon tetrachloride, and aqueous chloride ions.Halogenated hydrocarbons which may be treated by Ferragels include butare not limited to carbon tetrachloride, chloroform, vinyl chloride,dichloroethylene, perchloroethylene, tri-chloro ethylene, fluorinatedphenols, brominated phenols, chlorinated phenols, fluorinated alcohols,brominated alcohols, chlorinated alcohols, fluorinated alkanes,brominated alkanes, chlorinated alkanes, fluorinated alkenes, brominatedalkenes, chlorinated alkenes, polychorinated biphenyls, dioxanes such as2,2,4,4-tetrachlorodiphenyldioxane, as well as any combination thereofsuch as CFCs and CHFCs.

Ferragel materials are easily processed to form, for example,vitrifiable products for long term storage of contaminant materials. Forexample, silica-supported TcO₂ which may be formed when zero-valent ironon silica Ferragel is used to extract TcO⁴⁻ from waste streams, may beemployed in known vitrification processes to place radionuclides such asTcO⁴⁻ into long term storage. Ferragel materials can be employed in-situand left permanently in place, or used in a column or batch mode forlater recovery of the contaminant(s).

In an alternative embodiment as shown in FIGS. 7(a)-(c), modifyinglayers may be applied to Ferragel. The modifying layer may be applied tothe Ferragel to enhance the ability of the Ferragel to preferentiallyattract desired molecules or ions from a waste stream. The modifyinglayer may be formed from any of large hydrophilic cations sorbed ontothe surface of the Ferragel.

In this embodiment, the large hydrophilic cations may be provided from,for example, commercially available tetraalkylammonium ormethyltrialkylammonium salts such as methyltridodecylammonium iodide.These tetraalkylammonium or methyltrialkylammonium salts are sparinglysoluble in water but are soluble in alcohol. These salts may bedissolved in alcohols, preferably ethanol, and evaporatively depositedas films onto the Ferragel material to thicknesses of about 10 Å toabout 100 Å. These salts may be evaporatively deposited at from 55° C.to about 70° C. The specific salt that is deposited is selectedaccording to the species to be removed from the waste stream. Forexample, as shown in FIG. 7(a), tetraalkylammonium ormethyltrialkylammonium salts in which the alkyl is C₄ to C₁₈ may be usedto preferentially attract TcO₄ ⁻ from waste streams that include OH⁻,NO⁻, and NO₂ ⁻ anions. These compounds are available commercially fromchemical supply houses. These alcohol-soluble salts may be deposited asfilms of different thicknesses onto Ferragels by evaporating desiredsolutions using well known techniques.

In another embodiment of the invention, the modifying layer may beapplied as a thick coating of up to several millimeters thickness ontothe Ferragel. These thicknesses are achieved by using very large amountsof the above described ammonium salts.

In yet another embodiment, as shown in FIGS. 7(b)-(c), siloxane couplingfilms such as hexadecyl siloxane may be deposited on the Ferragel,preferably from alkyltrichlorosilane precursors, to films of thicknessesof about 10 Å to about 15 Å. Ferragel having siloxane coupling films maybe used to remediate halogens from halogenated hydrocarbons (FIG. 7(b)),and heavy metals from waste streams having a pH of about 5.5 or above(FIG. 7(c)).

What is claimed is:
 1. The method for remediation of heavy metals andhalogenated hydrocarbon contaminates from aqueous media comprising,forming a solution of a water soluble salt of Fe in water in thepresence of a support material, adding an alkali borohydride to thesolution to form a precipitate of zero valent Fe having a siloxanecoupling on the support material wherein the precipitate has an averageparticle size of about 5 nm to about 50 nm, and exposing the supportmaterial having the zero valent Fe thereon to an aqueous media having apH of 5.5 or above and having a contaminate selected from the groupconsisting of heavy metals and halogenated hydrocarbons to cause any oneof the heavy metals and halogenated hydrocarbons to deposit onto theprecipitate.
 2. The method of claim 1 wherein the heavy metals areselected from the group consisting of Cr, Th, Hg, Pb, Cd, As, Bi, andSb.
 3. The method of claim 1 wherein said halogenated hydrocarbons areselected from the group consisting of carbon tetrachloride,trichlorethylene (TCE), tetrachlorethylene (PCE), chloroform, vinylchloride, dichloroethylene, and perchloroethylene.
 4. The method ofclaim 1 wherein the water soluble salt of Fe is FeSO₄—7H₂O, the supportmaterial is silica gel and the alkali borohydride is NaBH₄.
 5. Themethod of claim 1 wherein said aqueous media is an organic liquid havingup to about 90% by weight water.
 6. The method of claim 5 wherein saidorganic liquid is selected from the group consisting of alcohols,ethers, and alkanes.
 7. The method of claim 1 wherein said aqueous mediais an organic liquid having up to about 50% by weight water.
 8. Themethod of claim 1 wherein the zero valent metal Fe has an averageparticle size of about 5 nm to about 15 nm.
 9. The method of claim 1wherein the precipitate consists essentially of zero valent iron havinga particle size of 5 nm to about 50 nm.